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INFRARED REFLECTIVE PIGMENTS Saket MulgeDhawal Unune
INTRODUCTIONPigments are inorganic or organic substances that are insoluble in water or the organic medium in which they are used as dispersions.Forty-five percent of the total solar energy is in the non-visible infrared region.Heat is a direct consequence of infrared radiation incident on an object. Infrared radiations range from 700 - 2500 nm wavelength. The heat-producing region of the infrared radiations ranges from 700 - 1100 nm. Excessive exposure may also lead to degradation of the materials.
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CHARACTERISTICSInfrared reflective pigments are complex pigments, which reflect the wavelengths in infrared region.The reflectivity and absorptivity of the pigment are independent of each other. Thus an IR reflective pigment may have any color.These pigments are highly stable and chemically inert, also stable to high temperatures.They even remain colorfast in the presence of strong acids, bases, oxidizing or reducing agents. Because of these properties, these pigments last as long as 30 years in outdoors. The most expensive component of the formulation is the IR reflective pigment.Monday, May 1, 2023
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MECHANISMIR reflective pigments do not absorb in near infrared region. They either reflect it or transmit it.Absorption of light occurs when light energy promotes electrons from one bonding state to another. If light of a different wavelength is used to cause this energy transition, it will not be absorbed.Iron chrome black (e.g.) There is no method to predict the IR reflectivity of an inorganic or organic compound. This property appears to be an inherent characteristic property
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FACTORS AFFECTING INFRARED REFLECTIVITYIndividual pigment selection.Dispersion.Blending pigments.Opacity.Contamination.Particle Size.
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SYNTHESISVarious attempts have been made to synthesize IR reflective pigments and coatings. The synthesis strategies can be roughly divided in three parts.1. Coating a thin film of glass or mica with an infra red reflecting substance and holding it there by physical forces. 2. Coating a thin film of glass or mica with a metallic surface. Metals are known to reflect almost entire visible and near IR radiations. 3. Synthesize inorganic crystalline substances, which have good pigmentary properties and find out if these are also IR reflective. The pigments are synthesized by subjecting mixtures of metal hydroxides, nitrates, acetates or even oxides, to very high temperatures in a process called calcination. Metal and oxygen ions in the solids rearrange to form new, more stable crystal structures such as spinel or rutile structures.(Temp-+1000°C)
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SYNTHESIS OF TiO2 Sulphate Process: 1. FeTiO3 (ilmenite)+ 2H2SO4 (60% excess) → FeSO4 + TiOSO4 + 2H2O.
2. TiOSO4 + (n+1)H2O → TiO2•nH2O + H2SO4. 3. TiO2•nH2O → TiO2 (Anatase or Rutile)+ nH2O. Chloride Process: 1. TiO2 + C → Ti + CO2 Ti + 2Cl2 → TiCl4 2. TiCl4 + O2 → TiO2 + 2Cl2
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Commercially available IR reflective pigment shades
TOTAL SOLAR REFLECTANCE (TSR)TSR is the total amount of solar energy that is immediately rejected by the surface material (e.g. coating). This term is a key figure to describe the heat build-up of surfaces.A high TSR indicates efficient reflection – a low TSR value indicates a strong tendency to absorb Near IR light and hence a significant heat build-up!It is useful to interpret the TSR value in relation to the matrix used and/or a reference pigment (e.g. titanium dioxide).
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Irradiation time [min]
Tem
pera
ture
[°C
]
Titaniumdioxide; max 43°C
P.Br. 29 (1); max 49°C
P.Bk. 30; max 55 °C
Carbon Black; max 63°C
Paint characteristic : Heat build-upMonday, May 1, 2023
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Paint characteristic : Total Solar Reflectance
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Wavelength [nm]
Ref
lect
ance
[%]
Titaniumdioxide; TSR 85%
Chromium Iron Oxide P.Br. 29 (1); TSR 21%
Chrome Iron Nickel Black Spinel P.Bk.30;TSR 9%
Carbon Black; TSR 5%
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ADVANTAGESLonger life-cycle due to less polymer degradation and thermal expansion due to lower temperature. Some are even used for about 25 years.Improved system durability and less thermal degradation.Reduced ‘Urban heat island effect’.Less heat to transfer into buildingsLow energy demand for air conditioning, particularly in equatorial regions.Cooler to touch for better handling.Aesthetically pleasing colors.Monday, May 1, 2023
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APPLICATIONSCoatings.Vinyl window and sliding.Cement, concrete and pavers.Automotive applications.Military applications.Infrared reflection from fire.
a.Coatings that do not burn when exposed to fire, generally referred to as "fire resistant“.
b.Coatings that insulate the flammable substrate, keeping its temperature lower than the combustion point, generally referred to as "intumescent".
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EXAMPLESTitanium Dioxide (TiO2).Cadmium Stannate (Cd2SnO4).Antimony oxy halide.Calcium carbonate.Crystalline and amorphous silicaSilicate minerals such as Talc, kaolin, calcined clay, wollastonite, nepheline syenite, feldspar, mica, attapulgite clay, bentonite.Organically modified bentonite, alumina trihydrate, aluminum oxides, barytes and lithopone.
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CURRENT AND FUTURE DEVELOPMENTSRefrigerated transport containers.Roofs of the buildings.The only technique to find out if a pigment reflects infrared radiations is to test its reflectivity.Only one compound of about 100 synthesized qualifies for a commercial pigment.Chlorophyll can be used as an excellent starting material for IR reflectivity study as it exhibits good reflectance, it is naturally available and abundant.
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TOP MANUFACTURERS
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Thank – you
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